Cone beam computed tomography (CBCT) is a developing imaging technique designed to provide relatively low-dose high-spatial-resolution visualization of high-contrast structures in the head and neck and other anatomic areas. It is a vital content of a dental patient's record. A literature review demonstrated that CBCT has been utilized for oral diagnosis, oral and maxillofacial surgery, endodontics, implantology, orthodontics; temporomandibular joint dysfunction, periodontics, and restorative and forensic dentistry. Recently, higher emphasis has been placed on the CBCT expertise, the three-dimensional (3D) images, and virtual models. This literature review showed that the different indications for CBCT are governed by the needs of the specific dental discipline and the type of procedure performed.

Imaging is a vital analytical appendage for the clinical evaluation of the patient. The overture of panoramic radiography in the 1960s and its widespread implementation lead to an upsurge in dental radiology by providing clinicians with a solitary broad image of jaws and maxillofacial structures.[1] Greek philosopher Plato in his work "The Republic" explained that instead of chaining prisoners in a cave, let us imagine radiologists in their darkened reading room, viewing shadows on light boxes or computer monitor screens rather than a cave wall.[2]

Alamri et al. analyzed different indications for cone beam computed tomography (CBCT), which are presided over by the needs of the specific dental discipline and the type of procedure performed via PubMed for publications related to dental applications of CBCT published between January 1998 and June 15, 2010 and found a total of 540 articles, 129 of which were clinically relevant and found that 34 (26.3%) related to oral and maxillofacial surgery, 33 (25.6%) to endodontics, 21 (16.3%) to implant dentistry, 15 (11.6%) to orthodontics, 12 (9.3%) to general dentistry, 7 (5.4%) to temporomandibular joints (TMJs), 6 (4.65%) to periodontics, and 1 (0.8%) to forensic dentistry.[3] Three-dimensional(3D) radiographic imaging has been widely adopted to relieve pains, but its application in dentistry has been narrow and restricted due to its cost, access, and dose considerations. The prologue of CBCT specifically devoted to maxillofacial imaging has led to a paradigm shift from 2-dimensional (2D) to 3D loom for image reconstruction and expanding the role of imaging from diagnosis to image guidance of operative and surgical procedures by way of third-party applications software.[1]

The development of CBCT technology reduces exposure using lower radiation dose as compared with conventional CT. The increase of speed for CBCTs has been swelling in number on the market over the past decade, and a variety of applications to the facial and dental settings have been established. As the demand for technology is increasing, soon the time will arise for the demand of craniomaxillofacial CBCT in the market.[4] CBCT allocates the conception of real time images in multiplanar reformation (MPR), that is, axial, coronal, sagittal, oblique, or curved image planes in comparison with thin-slice images of axial plane by conventional helical fan-beam CT.[5]

Historical Background

The history of invention of CBCT dates back to late 1970s when the Dynamic Spatial Reconstructor was developed by the Biodynamics Research Unit at the Mayo Clinic and was first adapted by them for potential clinical use in 1982. By early 1983, CBCT prototypes based on C-arms were demonstrated. CBCT provided an alternate method of cross-section image production to fan-beam CT using a comparatively less-expensive radiation detector than conventional CT. The technology transfer of CBCT to dentistry first occurred in 1995. Italian co-inventors, Attilio Tacconi and Piero Mozzo, developed a CBCT system (the NewTom DVT 9000) for the maxillofacial region that was designed and produced by QR, Inc of Verona, Italy. This unit became the first commercial CBCT unit marketed specifically to the dental market, initially introduced in Europe in 1999.

Initial interest focused primarily on applications in angiography in which soft-tissue resolution could be sacrificed in favor of high temporal and spatial-resolving capabilities. Exploration of CBCT technologies for use in radiation therapy guidance began in 1992 followed by integration of the first CBCT imaging system into the gantry of linear accelerator in 1999.

The recent review by Dorfler et al. on neurointerventional applications of CBCT is of particular interest to the field of neuroradiology.[6],[7],[8]

Advantages

Powerful low-cost computers and less expensive cone-beam X-ray tubes

High-quality flat-panel detectors lead to high spatial resolution

The images can be displayed as a full head view, as a skull view, or as a localized regional view

CBCT slices can be reformatted and viewed in multiple possible orientations

Cone beam produces a more focused beam and much less radiation scatter compared with the conventional fan-shaped CT devices. This significantly increases the X-ray utilization and reduces the X-ray tube capacity required for volumetric scanning

Dose-sparing technique is more superior as compared with alternative standard medical CT scans for common oral and maxillofacial radiographic imaging

Three dimensional visualization and geometrically accurate images with no superimposition of anatomical structures

Increased sensitivity and specificity for caries, periodontal, and periapical lesion

Patient comfort because there is no intraoral placement of film or sensor

Especially with larger field of views (FOVs), it is a limitation in image quality related to noise and contrast resolution because of the detection of large amounts of scattered radiation.[13],[14]

Clinical situations where cross-sectional imaging is used

Inadequate detection of relevant anatomical boundaries and the absence of pathology on clinical examination and conventional radiography

Need for adequate and better resolution for reference guidelines to minimize the risk of damage to anatomical structures, which are not obtainable when using conventional radiographic techniques

In clinical borderline situations where there appears to be limited bone height and/or bone width available for successful implant treatment [15]

The diagnostic information can be enhanced using radiographic templates, computer-assisted planning, and surgical guides.[16]

Principles

CBCT is an emerging technical advancement in CT imaging that uses cone beam acquisition geometry and flat panel detection (FPD) to provide relatively low-dose imaging with high isotropic spatial resolution acquired with a single gantry revolution

CBCT acquisition parameters can be optimized to produce isometric voxels as small as a 150 × 150 × 150 mm 3 at the isocenter

Most CBCT units for maxillofacial applications use an image intensifier tube/charge coupled device (IIT/CCD). Recently a system employing a flat panel imager (FPI) was released (i-CAT). The FPI consists of a cesium iodide scintillator applied to a thin film transistor made of amorphous silicon. Images produced with an IIT generally result in more noise than images from an FPI and also need to be preprocessed to reduce geometric distortions inherent in the detector configuration.[5],[16]

Equipment that requires the patient to lie supine physically occupies a larger surface area or physical footprint and may not be accessible to patients with physical disabilities

The four components of CBCT image production are acquisition configuration, image detection, image reconstruction, and image display.[1]

Dose

An understanding of conventional CT dose measurement methodology is important to recognize the limitations confronting many CBCT dosimetry studies

In an experimental C-arm model, Daly et al. found the effective dose for a head and neck CBCT scan of 16-cm head phantoms to be 0.1–0.35 mSv, depending on whether exposure parameters were optimized for bony or soft-tissue resolution. For reference, the expected effective dose of a typical Multi Detector Computed Tomography (MDCT) scan of the head is 1–2 mSv. An effective dose for sinus imaging in commercial dedicated head and neck CBCT scanners has been estimated to be approximately 0.2 mSv

De Vos et al. highlighted that there is complexity in making a detailed comparison of the various units due to variation in device properties, FOVs, detectors, frame rates, and the image quality required.[5],[16]

CBCT data

The tube and the detector perform one rotation (180° or 360°) around the preferred region leads to consequential prime data, which is later converted into slice data and viewed by user-defined planes

The CT volume consists of a 3D array of image elements known as voxels characterized with a height, width, and depth

The spatial resolution in a CT image depends on a number of factors during acquisition (e.g., focal spot, size detector element) and reconstruction (reconstruction kernel, interpolation process, voxel size)

Most machines support the digital imaging and communications in medicine (DICOM) format export. The images can therefore be used for most if not all the (software) applications utilized by conventional CT.[7]

Image detection

Current CBCT units can be divided into two groups, based on detector type: an IIT/CCD combination or a FPI

In CBCT imaging, voxel dimensions primarily depend on the pixel size on the area detector

The resolution of the area detector is sub-millimeter (range: 0.09–0.4 mm), which principally determines the size of the voxels. Therefore, CBCT units, in general, provide voxel resolutions that are isotropic (equal in all three dimensions)

Reconstruction times vary, depending on the acquisition parameters (voxel size, FOV, number of projections), hardware (processing speed, data throughput from acquisition to workstation computer), and software (reconstruction algorithms) used

Reconstruction should be accomplished in an acceptable time (<3 min for standard resolution scans) to complement patient flow

It is important to note that the various CBCT units come with standard viewing software, which will allow the dentist to examine the selected area of interest in all three planes: axial, coronal, and sagittal.[1],[4]

Data acquisition

In CBCT systems, the X-ray beam forms a conical geometry between the source (apex) and the detector (base) in comparison with conventional fan-beam geometry

CBCT works on the principle of Feldkamp algorithm, which is 3D adaptation of the filtered back projection method used in fan-beam 2D reconstructions. The process of filtering, or convolution, involves applying a kernel, or mathematic filter, to raw projection data before it is back projected. Filtering reduces the blur otherwise inherent in the process of back projection

The early Feldkamp algorithms solved the inversion problem for acquisition involving full circular rotation of the cone beam vertex about the object. More recent algorithms have been adapted for short circular arc trajectories of the X-ray source

A primary teleological difference between CBCT and MDCT is the isotropic nature of acquisition and reconstruction in cone beam systems

Cross-sectional imaging techniques are an invaluable tool during preoperative planning for complicated endosseous dental implant procedures.[6] Worthington highlighted that virtual planning of implant placement helps the clinicians to explore multiple treatment scenarios until the optimum treatment plan is attained and also allows the clinicians to create and visualize the end result before initiating treatment, which is accurate and cost effective and can be used to improve communication and coordination of a multidisciplinary team to achieve the desired clinical outcome.[11]

Based on the reported literature, CBCT measurement have been found to be more accurate than CT and their reformatted images provide the clinician with accurate 2D diagnostic information in all three dimensions, which helps the preoperative implant planning by use of imaging stent that helps to relate the radiographic image and its information to a precise anatomic location or a potential implant site. Moreover, once treatment planning is determined in the computer, it can be saved and applied to surgical sites by means of image-aided template production or image-aided navigation.[9]

Santos et al. highlighted that 3D-MPR view improves visualization of foramina anatomical relationship for postprocessing imaging by using Osiri X open source software of CBCT, which is realistic and recommended for preoperative planning.[17] The location and course of the mandibular canal and multiple mental foramina are vital structures, which should be taken into consideration for dental implant insertion or any surgical procedures involving the mandible. Naitoh et al. concluded from their study that resolution and visualization of the buccal foramen of the mandible in addition to the mental foramen by using CBCT images is better than helical CT images.[18] Naitoh et al. also evaluated differences between CBCT and multislice CT (MSCT) by detection of fine anatomical structures in the mandible and concluded that illustration of fine anatomic features in the mandible associated with neurovascular structures is consistent between CBCT and MSCT images.[19]

Role of CBCT in Periodontics

The use of CBCT in periodontology is mainly for diagnostic and treatment outcome. Based on literature, various authors highlighted that although periodontal bony defects are well visualized with CBCT but still conventional radiography manages to pay for higher quality bony contrast and delineation of the lamina dura.[6],[20] Vasconcelos et al. compared periapical radiographs with CBCT imaging in detecting and localizing alveolar bone loss by comparing linear measurements of the height, depth, and width of the defects and identifying combined bone defects in tomographic images.[21] Sun et al. revealed from their study that CBCT allows a more precise 3D examination of the defect with respect to traditional techniques, but unlike periapical radiography, it does tend to overestimate the defect. When the bone thickness is less than 0.4 mm, the size of the acquisition voxel, the height of the bone, is underestimated.[22] Vandenberghe et al. explored the diagnostic values of digital intraoral radiography and CBCT in the determination of periodontal bone loss, infrabony craters and furcation involvements and concluded that CBCT on the panoramic 5.2 mm reconstruction view allowed comparable measurements of periodontal bone levels and defects as with intraoral radiography. CBCT with 0.4 mm thick cross-sections demonstrated values closer to the gold standard, indicating more accurate assessment of periodontal bone loss.[23]

Role of CBCT in Endodontics

Prospective endodontic applications include diagnosis of endodontic pathosis and canal morphology, assessment of pathosis of non-endodontic origin, evaluation of root fractures and trauma, analysis of external and internal root resorption and invasive cervical resorption, and presurgical planning.[9] Leung et al. reported the various uses of CBCT like C shaped mandibular second molar teeth, extra root/canal, hidden radiolucency, presurgical assessment for apicectomy and is proved valuable for real time assessment in maxillo-facial trauma diagnosis and treatment.[13]

Perhaps the most important advantage of CBCT in endodontics is that it demonstrates anatomic features in 3D, reconstructs the projection data to provide interpretational images in three orthogonal planes (axial, sagittal, and coronal) with zoom magnification, window/level adjustments, and text or arrow annotation and has interactive capability for real-time dimensional assessment.[24] Most endodontic applications only require a small FOV (40 × 40 mm), which reduces dosage, scan time, and scatter artifacts, but it also focuses the volume on structures familiar to dentists.[9] The potential gift of CBCT is to scrutinize the cut of a single tooth of interest in the three planes of space thus making it more informative.[25] Aggarwal et al. studied the presence of accessory canals in furcation areas of 150 primary molars and permanentfirst molars by using CBCT and results showed that 36% permanent maxillaryfirst molars had accessory canals in the furcation area and while only 12% of primary mandibularfirst molars had accessory canals therefore CBCT can be used as accurate gold standard to detect the presence of accessory canals with clinical applicability.[26]

Simonton et al. evaluated differences in patient gender or age in relation to differences in the relative location of the inferior alveolar nerve (IAN) compared with the roots of the mandibularfirst molar. They found that females had significantly shorter vertical distances from the IAN to the mesial and distal apices and shorter horizontal distances for total width of mandibular bone at the mesial and distal apices. In addition, the overall width of the mandibular bone decreased in both genders from the third to sixth decade of life. Despite the provision of the third dimension, the spatial resolution of CBCT images (0.4–0.076 mm or equivalent to 1.25–6.5 line pairs/mm [lp/mm]) is inferior to conventional film-based (approx. 20 lp/mm) or digital (ranging from 8 to 20 lp/mm) intraoral radiography.[27]

Role of CBCT in Orthodontics

The applications of CBCT in orthodontics include assessment of palatal bone thickness, skeletal growth pattern, severity of tooth impaction, and upper airway evaluation for possible obstructions. CBCT is helpful in treatment planning of orthodontic cases that need buccal tooth movement and arch expansion.[6],[28] CBCT imaging is precise in the labial/lingual relationship, exact angulation of the impacted canine or supernumerary tooth, root resorption on the facial or lingual side of the tooth, more accurate volume of bone to place temporary anchorage device and mini-implant, condyle and ramus length for the occlusion, to evaluate mandibular asymmetry and degenerative changes visualization of TMJ osseous elements isolated (segmented) from other surrounding structures.[25] Using CBCT 3D hard and soft tissue segmentation along with photographic superimposition, orthodontists and other related specialists are able to simulate virtual patient and interact directly with the disease model, which improves the therapeutic outcomes in many clinical scenario.[29]

Determination of dental root morphology and volume is of immense clinical importance for biomechanical considerations. Liu et al. reported thatin vivo determination of tooth volumes from CBCT data is possible with a little deviation from the physical volumes by 4–7%.[30],[31] Chang et al. evaluated the relationship between changes in the alveolar bone density around the teeth and the direction of tooth movement by using CBCT around six maxillary anterior teeth before and after 7 months of orthodontic treatment in eight patients. They found that the bone density around the teeth reduced by 24.3 ± 9.5% and the direction of tooth movement is associated with the side of maximum bone density reduction and emphasized that CBCT is a useful approach for evaluating bone density changes around teeth induced by orthodontic treatment.[32]

Cervical vertebra is very useful in predicting skeletal age and useful input in determining growth potential, which aid in orthodontic treatment by correct diagnosis and treatment planning in relation to human growth and development. Hongjian et al. concluded from their study that CBCT volumetric data sets provides a 3D approach to the biologic aging of orthodontic patients by using images of the individual segmentation of cervical spine.[33] Mazzotta et al. highlighted that it is possible to create a 3D parametric CBCT model from 2D information of panoramic radiograph with a clinically valid accuracy level, which imitates the crown-root movement.[34] Halicioglu et al. studied mandibular third molar (3M)'s maturation in the crossbite and normal sides by 2D and 3D analyses using CBCT and they found no significant differences in the development of the 3Ms between the crossbite but the volume of 3M was found to be less in the crossbite side than in the normal side.[35]

Role of CBCT in Oral Diagnosis

The periapical index score (PAI) is commonly used to follow up the lesions in the bone using periapical radiographs. Recently, a new PAI based on CBCT was introduced known as CBCT-PAI.[36] Estrela et al. proposed new periapical index CBCTPAI based on measurements corresponding to periapical radiolucency interpreted on CBCT scans for identification of apical periodontitis (AP) in their study by using Planimp software in 3 dimensions: Buccopalatal, mesiodistal, and diagonal. The CBCTPAI offers an accurate diagnostic method for use with high-resolution images, which can reduce the incidence of false negative diagnosis, minimize observer interference, and increase the reliability of epidemiologic studies, especially those referring to AP prevalence and severity.[37] Esposito et al. reported in their technical report that CBCTPAI is modified clear cut reproducible method to assess periapical bone lesion follow up, which shows the reduction of the size of the lesion.[36]

Calcifications can be detected by using CBCT which are better than MDCT in depicting soft-tissue calcifications like carotid arthrosclerosis, tonsilloliths, and sialoliths. Small calcifications are important diagnostic clues for some cysts and tumors like Pinborg tumor, Calcifying odontogenic cyst or Gorlin cyst which are easier to identify on a CBCT scan than panoramic or intraoral radiographs.[10] Wahed et al. compared lesions associated with the salivary gland between conventional sialography and CBCT sialography and found that CBCT sialography was superior to conventional sialography in revealing stones, stenosis, and strictures, especially in the second and third order branches. They emphasized that CBCT sialography is advisable in obstructive salivary gland diseases for better demonstration of the ductal system of the gland.[38]

TMJ CBCT has created the boom in TMJ imaging by exploring and assessing periarticular bony defects, flattening, osteophytes, and sclerotic changes. Based on the systematic review by Hussain et al., who suggested that axially corrected sagittal tomography is method of choice in the detection of periarticular erosions and osteophytes.[6] Honey et al.reported the blinded observational cross-sectionalin vitro study of comparing the diagnostic accuracy of observers viewing images made with CBCT, TMJ panoramic radiography, and linear tomography (TOMO) by detecting cortical erosions affecting the mandibular condylar head. CBCT images provide superior reliability and greater accuracy than TOMO and TMJ panoramic projections in the detection of condylar cortical erosion.[39] Sumbullu et al. evaluated the articular eminence inclination and height in accordance with age and gender in TMJ dysfunction patients and healthy controls by using CBCT and they concluded that there were no statistically significant differences in eminence inclination and height according to gender. But the eminence inclination reaches its highest value between the ages of 21 and 30 years and shows a decrease after the age of 31 years in healthy patients. The eminence inclination was steeper in healthy control patients than in patients with TMJ dysfunction.[40] One of the key advantages of CBCT is to delineate the true position, translation and measurement of the condyle in the fossa and also helps to visualise soft tissue around the TMJ therefore CBCT imaging is preferred in cases of trauma, pain, dysfunction, fibro-osseous ankylosis and in detecting condylar cortical erosion and cysts. With the use of the 3-D features, the image guided puncture technique can be safely performed for TMJ disk adhesion.[41]

Role of CBCT in Oral Surgery

CBCT can be used in combination with 3D soft tissue data obtained with stereo photogrammetry, structured light systems and laser acquisition systems for diagnostic, treatment planning, and posttreatment evaluation purposes.[7]

Maxillofacial imaging is used for complex high-contrast bony structural pathology and craniofacial fractures. The intraoperative uses of C-arm CBCT systems has facilitated surgical navigation, localization of bony fragments, and evaluation of screw anchorage and plate fittings with low levels of metal artifact. Rafferty et al. emphasized on the application of C-arm CBCT imaging to endoscopic sinus surgery (ESS) and concluded that both spatial and soft-tissue contrast was sufficient to aid surgical navigation in the frontal recess.[6]

The anatomy of the greater palatine canal is very important for oral maxillofacial surgeons, and otolaryngologists for performing procedures in this area like administration of local anesthesia, dental implant placement, orthognathic Le Fort I osteotomy, and sinonasal surgery. Swirzinski et al. examined the anatomy of the greater palatine canal and found that the average length of the greater palatine canal was 29 mm (±3 mm), with a range from 22 to 40 mm. Coronally, the most common anatomic pattern consisted of the canal traveling inferior-laterally for a distance then directly inferior for the remainder (43.3%). In the sagittal view, the canal traveled most frequently at an anterior-inferior angle (92.9%).[42]

Role of CBCT in Forensic Dentistry

Dental age estimation methods are key elements in forensic as described in the literature. CBCT is used as noninvasive tool for age estimation based on the pulp/tooth ratio.[41] Yang et al. correlated between the chronological age of an individual and the pulp/tooth volume ratio of one of the teeth by a custom-made voxel counting software for calculating the ratio between pulp canal versus tooth volume based on CBCT tooth images of 28 single rooted teeth.[43] Jagannathan et al. assessed the pulp/tooth volume ratio of mandibular canines for age prediction in an Indian population by volumetric reconstruction of scanned images of mandibular canines in 140 individuals through CBCT and found it as a useful technique for age estimation.[44] Star et al. evaluated human dental age estimation method based on the ratio between the volume of the pulp and the volume of its corresponding tooth, which was calculated on clinically taken CBCT images from mono-radicular teeth and found that age is dependent variable and ratio as predictor of specific gender or tooth type with the obtained pulp/tooth volume ratios were thestrongest related to age on incisors.[45] Alam et al. evaluated the tooth size and arch dimension by 3D CBCT imaging through the effect age and gender differences. They found that the tooth size of the right and left side were similar except the second premolars. Largest variation in the tooth size were found in the upper lateral, second premolars, and lower lateral incisors in men, whereas the upper canine and lower incisors in women. Tooth size of the upper and lower canine showed the largest variation of sexual dimorphism. For the Arch dimension, the greatest variation was found in the inter-second premolar width of the upper arch followed by inter canine distance, and the inter-canine distance of the lower arch.[46]

Ilguy et al. evaluated preexisting CBCT images of adult females and males to provide data on foramen magnum and mandibular measures of sexual dimorphism for use as a reference sample in cases of establishing identity in unknown fragmentary skulls; based on their study, they suggested that sexual dimorphism can be assessed by the gonial angle and ramus, gonion-gnathion lengths, and bigonial breadth of the mandible and sagittal diameter of the FM on CBCT images.[47] Gamba et al. also evaluated CBCT mandibular images by measuring ramus length, gonion-gnathion length, minimum ramus breadth, gonial angle, bicondylar breadth, and bigonial breadth for the sexual dimorphism analysis and found that these variables are 95% correct for sex estimation and emphasized that these measurements can be used for sex determination in forensic settings.[48]

Facialreconstruction or approximation of human skeletal remains isfrequently essential for forensic identification. Behzad et al. describes a method of facial approximation that combines cephalometric techniques forcharacterization of the craniofacial complex with a database of CBCT skull images by analyzing anatomy of themastoid process, glabellar process, and frontal sinus area. They highlighted that this up-to-date modernmethod of CBCT facial approximation have shown that estimation of soft tissues from skeletaldata can be achieved by employing computationally and graphically complex techniques. It now also seems plausible to rapidly estimate the general shape of an unidentifiedskull's facial profile by comparison of the unknown skull's cephalometric data to those ina database of orthodontic patients.[49]

Guidelines

The American Academy of Oral and Maxillofacial Radiology (AAOMR) is in the process of developing evidence-based guidelines for appropriate application of CBCT. In the interim, the Executive Committee (EC) of the AAOMR considers it necessary to provide an opinion document addressing the principles of application of CBCT as it relates to acquisition and interpretation of maxillofacial imaging in dental practice. Guidelines rigid rules for requirements of practice and to establish a legal standard of care.[50]

Use of CBCT

CBCT imaging involves exposure of the patient to ionizing radiation. CBCT should be performed only by an appropriately licensed practitioner or certified radiologic operator under supervision of a licensed practitioner with the necessary training. CBCT examinations should be performed only for valid diagnostic or treatment reasons and with the minimum exposure necessary for adequate image quality.

Practitioner responsibilities

Practitioners, who operate a CBCT unit, or advice CBCT imaging, should have thorough understanding of the indications for CBCT as well as a familiarity with the basic physical principles, limitations, operational parameters, and the effects of these parameters on image quality, radiation safety and should be capable of correlating the results of these with CBCT findings with other alternative and complementary imaging and diagnostic procedures.

Documentation

Documentary evidence should be provided to demonstrate the diagnostic or treatment guidance need of the CBCT examination. Appropriate demographic, clinical, and case history information should be available to permit the proper performance and interpretation of the CBCT examination.

Radiation safety and quality assurance

Facilities operating CBCT should have specific policies and procedures for dose optimization. These include, but are not limited to, custom examination exposure protocols taking into account patient body size, field limitation to the region of interest, and use of personal protective devices such as a lead torso apron and, where appropriate, a thyroid collar. Procedures should follow all pertaining regulations.

Artifacts of CBCT

Any errorin the reconstructed image are depicted as (a) streaking, which is generally due to an inconsistency in a single measurement; (b) shading, which is due to a group of channels or views deviating gradually from the true measurement; (c) rings, which are due to errors in an individual detector calibration; and (d) distortion, which is due to helical reconstruction.[51]

Metal in a patient's mouth has been shown to cause artifacts that can interfere with the diagnostic quality of CBCT. Recently, a manufacturer has made an algorithm and software available that reduces metal streak artefact (Picasso Master 3DH machine; Vatech, Hwaseong, Republic of Korea). Bechara et al. reported from their study that enhanced and superior images can be obtained when the metal artefact reduction algorithm (MAR) is used based on reduced profile lines variation at gray level changes and area histograms have increased contrast-to-noise ratio.[52] Hunter et al. demonstrated cupping effect artefact on the Planmeca Promax 3D CBCT unit (Planmeca OY, Helsinki, Finland) by using uniform aluminum cylinder (6061), which was analyzed by using a line profile plot of the gray level values using Image J software (National Institutes of Health, Bethesda, MD) and a hardware-based correction done by using copper prefiltration to reduce beam hardening artifact and a software-based subtraction algorithm was used to prevent scatter contamination. The outcome of the study showed that the hardware-based correction only suppressed the beam hardening, which causes cupping effect artifact, but the software-based correction helps in elimination of the cupping effect artifact; therefore, altogether they improve gray level uniformity in CBCT.[53] Artifacts are classified according to their cause:[1]

X-ray beam artifacts: They arise from the inherent polychromatic nature of the projected X-ray beam known as beam hardening effect, which causes cupping artifact due to distortion of metallic structures by differential absorption and streaks with dark bands that can appear between two dense objects

Patient-related artifacts Patient motion leads to misregistration of data, which causes unsharpness in the reconstructed image, and can be minimized by using a head restraint and short scan time as much possible. The presence of dental restorations in the FOV causes severe streaking artifacts due to extreme beam hardening effect and sometimes photon starvation causes horizontal streaks in the image and noisy projection reconstructions

Scanner-related artifacts: It occurs due to imperfections in scanner detection or poor calibration which causes circular or ring-shaped artifact.

Medicolegal Issues Related to Cbct

As there is saying that anything new has its own criticism as well as acclaim with the advent of CBCT into dentistry has plentiful advantages but still have potential pitfalls regarding medicolegal issues like who may own and operate the machines, for what purposes should the machines be used, how broadly or narrowly should the field be collimated.[54] Depending on the manufacturer and model, a CBCT machine is costlier in comparison to conventional radiography that triggers the practitioners to achieve a return on investment by over-prescription of procedures, which is unethical and has prompted legislation on limiting Medicare payments for self-referral services.[28]

Medicolegal issues are also related to the acquisition and interpretation of CBCT data because in many clinical situations that needs wider FOV to capture all maxillofacial structures within the volume. Therefore it is triggering spark among oral and maxillofacial radiologists that dentists without proper training should not perform or interpret CBCT data without extensive knowledge of various maxillofacial structures as well as training in cross-sectional anatomy, which is very essential for interpretation in detail in order to prevent any overlook to potentially life-threatening lesion.[9]

Controversy

As with any other emerging imaging technology, use of CBCT is a debatable topic because of lack of user experience. Additionally, the ACR Practice Guideline for CT of the head and neck recommends that all imaging studies should evaluate bone and soft-tissue algorithms but due to low radiation dose, CBCT can only provide clear bony detail in comparison to soft tissues

Point-of-service imaging and other self-referral services, however, have been widely criticized for encouraging overuse and directly inflating medical costs. The belief that financial incentives undermine the clinical decision-making process has been the basis for federal legislation limiting Medicare payments for self-referral services (so called "Stark laws")

The advent of CBCT technologies has also fueled the controversy surrounding office-based imaging, which is usually performed and interpreted by nonradiologists often without the accreditation, training, or licensure afforded by the radiology community.[6]

Conclusion

In this modern era, CBCT is a promising CT technology which has become a diagnostic tool for the dentists and otolaryngologist due to its prospective applications of high-contrast structures in the head and neck as well as dentomaxillofacial regions at comparatively low patient dose. Rapid development of CBCT is dyed-in-the-wool of dentomaxillofacial imaging for 3D radiographic assessments in routine clinical dental practice. It provides clinicians with sub-millimeter spatial resolution images of high diagnostic quality with relatively short scanning times (10–70 s) and less radiation dose equivalent to that needed for 4–15 panoramic radiographs. Skilled oral and maxillofacial radiologists play a pivotal role in extracting extensive information available in the CBCT data set for thorough and knowledgeable interpretation.